The receptor activator of nuclear factor KB (RANK), receptor activator of nuclear factor KB ligand (RANKL), and osteoprotegerin (OPG) triad (RANK/RANKL/OPG) play an important role in immune response and bone metabolism. RANK/RANKL triggers a network of TRAF-mediated kinase cascades that promote osteoclast differentiation. RANKL is expressed on osteoblast cells and its receptor, RANK, on pre-osteoclastic cells. The RANK/RANKL interaction induces the differentiation and formation of multinucleated mature osteoclasts, causing bone resorption. The third protagonist, OPG, is also produced by osteoblasts and exerts an inhibitory effect on the pre-osteoclastic differentiation process. OPG, by binding to RANKL, inhibits the RANK/RANKL interaction and subsequent osteoclastogenesis.